158 College of Forestry 
(9) The properties of the extracts obtained respectively 
from sound and decayed hickory wood indicate that, in the 
course of the decomposition, a portion of the carbohydrate 
substance, particularly the hemicellulose xylan, becomes con- 
verted into humic substances of two principal groups, 
namely, humic acid and humin. It is the accumulation of 
these humie substances which gives rise to the dark brown 
decomposition products which are of such common occurrence 
in decaying wood. 
(10) Humic acid and humin were produced artificially 
from the carbohydrate substance of the sound hickory wood 
by boiling with a mixture of strong hydrochlorie acid and 
potassium chlorate. The substances thus produced indicate 
close relationship with the humin-hke decomposition products 
formed as black zones in decaying wood. 
(11) The chemically resistant by-products, often forming 
blackish zones in wood decayed by Polyporus pargamenus, 
have proved to be a group of substances analogous to or 
nearly identical with those substances concerned in the 
brownish discolorations in dead wood that is entirely free 
from fungous attack. The formation of the brown decom- 
position products in the latter case likewise is a sign of the 
humification which gradually sets in when the cell contents 
become dessicated or when their walls or contents undergo 
decomposition. This humification is greatly ‘accelerated by 
the presence of wood-rotting fungi which greatly hasten the 
decomposition. 
Chemical Affinity of the Brown Decomposition Progen — 
Now that the source of the decomposition product has been 
indicated, it is advisable to consider its final chemical 
nature. In the discussion of the chemical composition of 
the cell-wall the elaboration of those changes of tissue 
substances — celluloses and compound celluloses — which 
accompany or follow the cessation of vital activity has 
been deferred purposely until this point. It is more dif- 
ficult to apply the term “death” to the vegetable than to 
the animal organism. In the sense of the “elaboration of 
